The field of the invention relates to nuclear waste and more particularly to methods of determining a content of nuclear waste containers.
Since the advent of the nuclear age, nuclear waste has been a significant impediment to the development of nuclear technology. In the last fifty years, nuclear waste has accumulated in significant quantities.
Nuclear waste is different than other types of waste in that it can kill without direct contact through the effects of radiation. Because of radiation, nuclear waste must be either shielded or stored in protected areas.
While shielding is effective, it also creates additional difficulty in storing and moving waste containers. It also adds to the bulk of storage containers.
When nuclear energy first became a factor during World War II (and to a lesser extend even now) nuclear waste was handled in a manner similar to other wastes. What makes nuclear waste more difficult to process than other wastes, however, is the difficulty of identifying and classifying the contents of nuclear waste containers.
In the past, the accepted method for identification of container content has relied upon the non-destructive examination of nuclear waste drums using x-ray inspection and real-time radiography (RTR). Standard RTR techniques have included the use of 450 kV (or less) constant potential x-ray sources. Image intensifiers have been used as live radiographic detectors for the video taping of drum content.
The use of RTR could be improved by varying the x-ray voltages and currents to optimize the viewing contrast for differing drum content. However, RTR still has limited inspection capability for the imaging of dense waste drum content like metals, cements and sludge because of the lack of x-ray penetration at 450 kV and a lack of dynamic range for an image intensifier of the x-ray detector. To aid in the analysis of nuclear waste, the Department of Energy (DOE) has published a number of procedures explaining the use of RTR for inspection for nuclear waste drums.
The limitations of RTR methods may be discerned from a recent RCRA permit from the state of New Mexico for the DOE""s WIPP site. The permit states that drums, which cannot be inspected by RTR (e.g., lead lined drums) must be opened for direct invasive inspection by visual examination. Invasive examination is much more costly than the method discussed below because of the need for operator protection from radiation using a protective enclosure (e.g., a glove box).
Since WWII thousands of nuclear waste containers have been filled and stored in a limited number of locations without regard to what such containers have stored inside them. In order to resolve the problem of nuclear waste, an effort must be made to classify nuclear waste as a first step in finding a final solution to disposal of such waste. Accordingly, a need exists for a safe and more reliable means of identifying and classifying nuclear waste.
A method and apparatus are provided for identifying a content of a nuclear waste container. The method includes the steps of forming an image of the contents of the container using digital radiography, visually comparing a content of the image with an expected content of the container and performing computer tomography on the container when the visual inspection reveals an inconsistency with the expected content.